ES2170653B2 - ROBOTIZED CIRCULAR TABLE FOR THE POSITIONING OF PARTS OR OBJECTS. - Google Patents

Abstract

Robotic circular table for positioning pieces or objects housed in a pallet on its periphery in the work area of machines and installations. Composed of a tree vertically arranged by means of two internal transverse bearings that engage it without friction to an axis housed inside and threaded at one end to fix it as a bolt to a base platform on which the tree also rests by means of an axial bearing. A stepper motor through a gear jump provides the torque. The maintenance torque of this motor sets the position of the table acting as an electromechanical brake, the switching sequence for its phases is provided by a programmable automaton. The table consists of the corresponding position and speed sensors. The position sensor is absolute which allows orientation with respect to a reference in the system connection.

Description

Robotic circular table for positioning of pieces or objects.

The patent is registered in the technical sector electromechanical and refers to a new circular table prototype robotic carousel type for positioning and displacement of the pieces or objects, located on the pallets of its periphery, in the work area of other machines or installations following a certain cycle

Have an automatic transport machine the parts from the general manufacturing line to the vertical Working head of a machine tool assumes in general the ability to effectively manage the flow of parts and make The most flexible manufacturing process. For this the table stores temporarily on the pallets of your carousel the total pieces or partially processed before returning them to the general line. The  pieces move to different positions by turning the carousel following a certain cycle or sequence governed by A programmable automaton.

In other applications of the robotic table such As commercial exhibitors, pallet objects are move along the circular path and reach sequentially the front position of the exhibitor each of them, the table keeps them in that position for a while determined.

The robotic circular tables are built usually from a mechanical device called indexer based on an eccentric cylindrical cam system and roller trackers on the carousel that is driven by an engine asynchronous with brake. Replace this device with a jump of gears driven by a stepper motor, whose assembly operability is equivalent, supposes:

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Do more Compact and reliable mechanical system.

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Improve their precision that is now a function of the number of steps per lap of the engine and gear reduction in gear jump.

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Dispose of a pair of maintenance at zero steps / s provided by this type of engine that makes the mechanical brake unnecessary to maintain a table position.

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 Reduce the table cost.

In the auxiliary automotive industry dedicated to the manufacture of homokinetic joints is necessary to perform different operations on the joint sleeve. For this the sleeves must be positioned in the vertical working head of various machine tools: centering machines, tempering machines, etc.

The maintenance of the individual machines is made with tables of this type that load a hose from the general line to process it in a machine tool determined, and then return it to the line.

On the other hand machines are also used this type as commercial exhibitors and in general in any application in which a type transport system is necessary Carousel to move objects.

The machine object of this invention patent, whose general scheme is presented in figure 1 allows to move circularly the pieces or objects placed a circular plate swivel or carousel that is supported by four wheels with bearing in a cylindrical frame as indicated in the figure. This carousel is solidary to a tree. By turning it shaft that is a consequence of the torque applied by a motor without brushes with permanent magnet rotor through a jump of gears indicated in figure 3, a position is reached angular determined. The maintenance pair itself of this type of engine at zero steps per second keeps it.

The machine consists of two systems: the set mechanic explained in Figures 2 and 3, and the electronic system of control.

The electro-mechanical assembly that It can be seen in Figures 2 and 3 is formed by:

(one).

A base to which it has been drilled to attach a vertical axis as a Bolt In addition other drills serve to fix the supports of the engine, sensors and the base supports themselves.

(2).

A threaded shaft in one end, by which it is fixed to the base. This axis is responsible for  provide verticality to the tree (3) so its length is greater than 1 / 3H, where H is the height of said tree as indicated in the exploded view of Figure 3.

(3).

A tree that is the dynamic element of the set, which has been practiced a inner hole with two different diameters the first of the which of larger dimension houses two transverse bearings (8) that are crossed by the axis (2) and that is also housed in the inner hole practiced on the tree without making contact with it. In other words, the axis provides verticality to the tree through the cross bearings concentrically locked to both of them.

(4).

A bearing axial arranged at the base of the tree between it and the base platform which reduces as much as possible the friction losses at the base From the tree.

(5).

A plataform circular which is the rotating carousel in solidarity with the tree by Allen screw. The pallets are housed in their periphery circular or by screws on the outer edge.

(6).

A pinion (in the 20 teeth prototype and module 1) integral to the motor shaft using captive thymes at least two located at 180 °

(7).

A crown (in the 80 teeth prototype and module 1) or gear to which it is practiced an inner hole equal to the smaller outer diameter of the shaft and united with this one by means of captive thymes, at least two, at 180 degrees.

(8).

Two bearings Radials that attach the shaft to the shaft providing verticality to the first without introducing a significant friction torque.

(9).

An engine without brushes (brushless) whose rotor is formed by a number determined from permanent magnets. Two coils of its stator are applies the electrical power that makes the pairs of poles of this mechanically displaced half the distance between poles Opposites are alternately excited. The interaction between rotor and stator causes the rotor to move 1/4 of the step between poles in each polarity change of the winding.

(10)

An automaton programmable that governs the switching sequence for the phases the motor.

(eleven).

Opto-coupler tachometric sensor

(12).

Headband opaque-translucent tachometric sensor.

(13).

Potentiometer.

(14).

Coupled pinion to the potentiometer that engages in the crown of the tree.

(fifteen).

Converter Digital-Analog

(16).

Stage amplification.

(17).

Frame cylindrical on which the wheels of the circular platform are supported upper swivel.

(18).

Nut fixing the wheel with bearing to the bolt that attaches it to the carousel.

(19).

Wheel with bearing attached to the carousel that supports it on the frame also allowing rotation.

(twenty).

Bolt that connect the wheel to the carousel.

(twenty-one).

Allen screw which fixes the carousel to the tree causing the movement of both be solidary, this screw has no contact with the cylindrical frame.

(22).

A nut that fix the axis to the base in which a circular pocket has been made to arrange said nut internally.

(2. 3).

Nut fixing the motor to the base fixing flap.

(24).

Screw fixing the fin to the base.

(25).

Fin fixing the potentiometer to the base.

(26).

Key semicircular that couples the crown to the tree.

The precision in the positioning of the table is function of the number of steps per revolution of the motor (9) and the number of pinion teeth (6) and crown (7). For the stepper motor bipolar 48 steps per lap installed in the prototype, when the motor excitation is in full step each step represents a tree twist of:

\ theta_ {tree} = \ theta_ {engine} = \ frac {Z_ {pinion}} {Z_ {crown}} = 7'5 ^ {o} \ cdot \ frac {20} {80} = 1.875 o

In which:

Z_ {pinion}: Number of teeth of the coupled pinion to the engine

Z_ {crown}: Number of teeth of the crown coupled to the tree.

\ theta_ {tree}: angle rotated by the tree.

\ theta_ {engine}: angle turned in one step Complete by the engine.

On the other hand when the motor excitation is in half a step the corresponding discrete turn of the pinion is half 3'75 ° and therefore the corresponding rotation of the solidarity crown the tree is worth:

\ theta_ {tree} = \ theta_ {engine} \ frac {Z_ {pinion}} {Z_ {crown}} = 3'75 ^ {o} \ cdot \ frac {20} {80} = 0'9375 o

This is the best positioning accuracy of the table that can be obtained with the engine and transmission installed in the prototype made.

A programmable automaton (AP onwards), constitutes the electronic table control system, and provides the switching sequence necessary for the phases of the engine. The frequency at which said switching occurs determines the engine speed and angular speed of the table. As the AP cycle time, constant is selected and equal to 7 [ms] in the prototype, the switching frequency is Fixed value 142 [Hz] the inverse of the cycle time. In these conditions the angular velocity of the table once the movement is also constant.

The position sensor is absolute which allows to the table orient with respect to an external reference, which corresponds to a certain value provided by the sensor, in The electronic control system connection, this sensor is potentiometric type. The potentiometer shaft (13) has been fixed a pinion (14) that is driven by the gear of the tree. For the both the angle rotated by the cursor and its analog voltage is directly proportional to the angular position of tree and carousel They are supportive. That is to say the information of the position of the table carousel from an analog signal that It is processed by a data acquisition card. This card converts said signal into a digital output value with levels of voltage and current compatible with the digital input channel of the AP. This card has two stages:

The first data acquisition formed by a digital analog converter (ADC 0808) performs a conversion ratiometric of the analog variable to be measured in a digital value which is a percentage of the maximum scale value that is not referenced to an absolute standard. Input voltage provided by the potentiometer to the digital analog converter It is expressed by the equation:

\ frac {V_ {IN}} {V_ {ES} - V_ {Z}} = \ frac {D_ {X}} {D_ {MAX} - D_ {MIN}}

In which:

V_ {IN} = Input voltage to ADC0808. V_ {ES} = Maximum value of the stress scale. V_ {Z} = Tension or zero voltage, voltage reference. D_ {X} = Data to measure. D_ {MAX} = Fact corresponding to the upper limit of to size. D_ {MIN} = Data corresponding to lower limit to measure.

In the second stage the digital outputs of the ADC0808 converter are coupled to the AP input channel by an amplifier whose voltage and current levels are referenced to the voltage and current reference of the channel AP entries.

The control program compares the data of the current table position provided by the position sensor with the setpoint entered in the control system. If it exists difference between the two, that is to say a position error, the AP sends the switching signals necessary for motor movement they turn the table carousel until its position Snapshot is equal to the setpoint. AP control program Solving this function is structured in two modules:

The first acquires the position data snapshot and compares it (algebraic difference) with the slogan, The result determines the direction of rotation of the motor.

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The second module of the program sends the sequence switching to the stepper motor. This switching sequence is stored and encoded in the AP memory in a table whose values correspond to the transistors of the bridge in (H) of the amplification card to be saturated -passing conduction- to switch the direction of the current in the phases the motor. The increasing or decreasing direction in which it traverse those positions of the table in the AP memory determines the direction of rotation of the hourly or anti-clockwise motor and therefore through mechanical transmission also that of the table.

On the other hand the table is able to decelerate a few degrees before reaching a position, approximately Five Grades. This is possible thanks to an internal oscillator associated with the AP scan cycle that is active in cycles Alternative Under these conditions the AP sends sequences of switching to the engine only in one of every two cycles in this way the angular velocity is halved.

Claims (5)

1. Robotized circular table for the positioning of parts or objects characterized in that a bipolar stepper motor rotates a vertically arranged shaft by means of a gear jump thanks to two internal transverse bearings that engage it without friction to a threaded inner shaft at its end bottom to fix it as a bolt a base platform on which the shaft is also supported by an axial bearing. The table consists of the corresponding position and speed sensors. The position sensor is absolute which allows the table to be oriented with respect to an external reference in the connection of its electronic control system, this sensor is of potentiometric type. A pinion has been fixed on the axis of the potentiometer, which is driven by the crown attached to the shaft. The analog signal provided by the potentiometer is proportional to the angle turned by the table carousel. This signal is converted to a digital value that is transmitted to the programmable controller. Said programmable automaton generates the switching sequence for the motor phases from a table of coded values corresponding to the transistors of the bridge in (H) of the amplification card that must be saturated to switch the direction of the current in the phases the motor. The increasing or decreasing direction in which these positions of the table are traversed in the memory of the programmable automaton determines the direction of rotation of the time or anti-time motor and therefore through the mechanical transmission also the direction of rotation of the carousel of table. 2. A robotic circular table according to claim 1, characterized in that the stepper motor of its electric drive provides a zero-step / second maintenance torque capable of fixing the position of the table acting as an electromechanical brake. 3. A robotic circular table according to claims 1 and 2 characterized in that it is provided with an amplification card that performs the current switching in the phases of a bipolar stepper motor by means of a bridge in (H) of transistors connected to the outputs of control of a programmable automaton with a matrix of darlington amplifiers. 4. A robotic circular table according to claims 1 to 3 characterized in that it is provided with a potentiometric absolute position sensor, which converts the analog voltage of the potentiometer cursor proportional to the position of its axis, to which a pinion is engaged that meshes with the crown of the tree, in a digital value by means of a digital analog converter whose outputs are adapted by means of opto-couplers to the voltage and current levels of the inputs of a programmable automaton. 5. A robotic circular table according to claims 1 to 4 characterized in that it is provided with a speed sensor formed by a belt with a certain number of opaque-translucent bands installed on the edge of the carousel that crosses an interruptible beam opto-coupler. From the spatial geometry of this sensor, a square signal is obtained with the rotation of the table whose frequency is proportional to its angular velocity.